Bathonian

In the geologic timescale the Bathonian is an age or stage of the Middle Jurassic. It lasted from approximately 168.3 Ma to around 166.1 Ma (million years ago). The Bathonian age succeeds the Bajocian age and precedes the Callovian age.

The Bathonian stage takes its name from Bath, a spa town in England built on Jurassic limestone (the Latinized form of the town name is Bathonium). The name was introduced in scientific literature by Belgian geologist d'Omalius d'Halloy in 1843. The original type locality was located near Bath. The French palaeontologist Alcide d'Orbigny was in 1852 the first to define the exact length of the stage.

The base of the Bathonian is at the first appearance of ammonite species Parkinsonia (Gonolkites) convergens in the stratigraphic column. The global reference profile for the base of the Bathonian (a GSSP) was ratified as Ravin du Bès, Bas-Auran area, Alpes de Haute Provence, France in 2009. The top of the Bathonian (the base of the Callovian stage) is at the first appearance of ammonite genus Kepplerites.

In the Tethys domain, the Bathonian contains eight ammonite biozones:

Members of the order ammonitida are known as Ammonitic ammonites. They are distinguished primarily by their suture lines. In ammonitic suture patterns, the lobes and saddles are much subdivided (fluted) and subdivisions are usually rounded instead of saw-toothed. Ammonoids of this type are the most important species from a biostratigraphical point of view. This suture type is characteristic of Jurassic and Cretaceous ammonoids but extends back all the way to the Permian.

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